Analysis of lipsticks by ART FT-IR microspectroscopy

The slide-on Ge µIRE and the slide-on diamond µIRE for ATR FT-IR spectral acquisition with an infrared microscope were employed for molecular characterization of trace lipstick smear on various surfaces. Due to the small sampling area of the IREs, a small quantity of lipsticks can be analyzed. The spectra acquired by diamond µIRE and Ge µIRE were in good agreement to those acquired by conventional ATR technique. In this work, commercial lipsticks from various manufactures were investigated. Direct correlation between the molecular structures and the infrared absorptions enable the identification of lipstick based on the observed ATR FT-IR spectra of the trace lipstick smear. The “contact-and-collect” operation was employed for transferring the trace lipstick onto the tip of the IREs. A minute smear of lipstick on the μIRE can be analyzed while the chemical information of lipsticks on various substrates was obtained without any interference from the substrate. The operation was non-destructive and could be performed without an additional sample preparation. This method is suitable for the unique identification of minute lipstick amount as well as forensic analysis.

本研究采用搭载于红外显微镜的可滑动式锗基微内部反射元件 (slide-on Ge µIRE) 与可滑动式金刚石基微内部反射元件 (slide-on diamond µIRE)，开展多种基底表面微量口红痕迹的衰减全反射傅里叶变换红外 (Attenuated Total Reflection Fourier Transform Infrared Spectroscopy, ATR FT-IR) 光谱采集与分子表征。由于内部反射元件 (Internal Reflection Element, IRE) 的采样区域较小，可实现微量口红样品的分析检测。金刚石基微内部反射元件与锗基微内部反射元件所采集的光谱，与常规衰减全反射技术所得光谱具有良好的一致性。本研究对来自多家厂商的市售口红进行了分析测试。通过分子结构与红外吸收峰之间的直接关联，可基于观测得到的微量口红痕迹衰减全反射傅里叶变换红外光谱实现口红的鉴别。本研究采用‘接触采集’ (contact-and-collect) 操作，将微量口红痕迹转移至内部反射元件的尖端。可对微内部反射元件表面的微量口红痕迹进行分析，同时获取不同基底表面口红的化学信息，且不受基底的任何干扰。该操作无需额外的样品前处理步骤，且具备非破坏性。本方法适用于极微量口红样品的精准鉴别以及法医分析。